A major issue for industries that use bulk materials is
storage and ease of conveyance. Since bulk materials are heavy and difficult to
handle, they require special equipment to transfer them into storage and from
storage to production. A method that has been designed by engineers uses a
simple feed screw type mechanism that moves materials in appropriate quantities
from silos and hoppers to production. These specially feed screw devises are
known as screw feeders or screw conveyors.
What is a Screw Feeder?
A screw feeder moves materials along a set of flights during
its rotation using the feed screw design. When fully loaded, each flight
contains exactly the same amount. New material can only be introduced to the feed
screw mechanism through the first flight, which is located directly under the
The transport mechanism of a screw feeder depends on the
friction between the product and the feed screw blades, tube, and the product.
The capacity of the feeder depends on the angle of the blades, which is defined
by their pitch and the diameter of the screw. Another factor is the diameter of
the core that determines the content of a pitch.
The pitch of a screw feeder has three characteristics, which
are its minimum, optimum, and maximum. Each of these factors depend on the core
diameter, screw diameter, and the unique characteristics and properties of the
product to be moved. Of the three traits of the pitch, optimum is the one that
is most important since that is where the screw mechanism functions the best.
Types of Screw Feeders –
As with any type of conveying equipment, screw feeders have
to be engineered and designed to specifically fit the type of material and
product that they are conveying. The type of feeder for granular products
varies from the type of feeder used for powdered products. This diversity in the
types of products creates the diversity in the types of feeders.
In variable pitch feeders, the pitch of the screw varies
from shorter to longer as it moves along to the discharger. The pitch variation
begins at the inlet where it is the smallest and increases in length as it
moves along creating more volume for the addition of materials from the hopper.
A tapered outside diameter feeder is similar to the variable pitch version and
is tapered from the inlet opening.
The mass flow version of a feeder combines the
characteristics of the variable pitch version and the tapered version. The
tapered section is in the middle of the screw away from the inlet. This allows
for variable volumes of material be fed from the hopper. The variable pitch is
added where the cone end shape ends and continues to the discharge.
Benefits of a Screw Feeder –
More and more industries that have powder, granular, or
flaky materials are switching to screw feeders for the movement of raw
materials. Material handling engineers and designers are finding that this type
of technology provides a more consist form of raw material supply at a better
The major benefit of a screw feeding mechanism is its
longevity. As every material management engineer can tell you, other forms of
conveying devices are fragile, tend to get damaged, and breakdown. The unique
nature of a screw system is the durability of its materials, which are tough,
resilient, and solid.